The present invention relates generally to contact lenses and, more particularly, to a contact lens having a generally flat central posterior surface and to a method of making such a contact lens.
Approximately 10 to 15 years ago a surgical procedure was developed in the Soviet Union and in Columbia for correcting myopia. This procedure, radial keratonomy, involves making multiple radial incisions through four of the five layers of a patient's cornea which cause the central portion of the normally spherical cornea to deflate and flatten. When successful, the procedure reduces the effective power of the eye as a lens, increasing the visual acuity of the myopic patient. Successfully treated patients no longer require eye glasses or contact lenses to correct their myopia.
Myopia is generally regarded not as a disease but rather as an inherited trait or congentital defect. Radial keratonomy is usually regarded as a cosmetic procedure rather than as treatment for a disease. It is an elective procedure which often permits the patient to dispense with both the eye glasses which the patient may regard as unattractive and with the discomfort and inconveniences sometimes associated with wearing contact lenses.
Unfortunately, the the radial keratonomy procedure is not a unmitigated success in every case. Radial keratonomy does not correct astigmatism which is associated with asymmetry of the posterior surface of the cornea or asymmetry of the crystalline lens. Further, the radial keratonomy procedure may result in instability of the central portion of the cornea causing the patient's visual acuity to vary from hour to hour during the day as the radius of curvature of the central portion of the cornea changes. While astigmatism of a patient who has undergone radial keratonomy can be corrected with eye glasses, this approach to treatment is highly impractical for the patient suffering from corneal instability. Such a patient would require several pairs of glasses to see correctly throughout the day due to the variations in visual acuity.
Other types of surgical procedures such as penetrating keratoplasty (corneal transplant used in treating corneal disease) or corrective surgery for Fuchs corneal dystrophy may also result in a centrally flattened cornea. Patients with corneas having a surgically flattened central surface generally cannot be well fit with prior art corrective contact lenses.
Thus, there is a need for a device or method which can correct the problems associated with the corneal instability which sometimes occurs after radial keratonomy. Further, there is a need for a contact lens which can correct conditions which reduce visual acuity such as astigmatism which are not successfully treated by the radial keratonomy procedure, or which remain after or result from other surgical procedures such as penetrating keratoplasty.
Prior art contact lenses, which typically have a generally concave posterior surface, cannot be successfully fitted to or be worn by the radial keratonomy patient. For example, if the posterior surface of the contact lens is fit to the generally normal portion of the cornea surrounding the flat central surface, a hard or gas permeable contact lens will cause trauma and swelling of the cornea. However, if the posterior surface of a prior art hard or gas permeable contact lens is fit to the central surface of the cornea, the contact lens will be unstable and will tend to ride up or down, lift off and irritate the cornea.
Further, if the posterior surface of a large soft lens is fit to the normal portion of the cornea surrounding the central flat corneal surface, the lens will tend to buckle proximate the central surface of the cornea, resulting in poor vision and symptoms indicating the lens fits the cornea too tightly. If the patient is fitted with a scleral or haptic lens of traditional design, air bubbles will tend to form under the lens proximate the central portion of the cornea and the lens will feel too tight even if the lens is provided with holes for tear flow. In short, traditional lens designs do not meet the requirements of a patient who has undergone radial keratonomy.
The present invention meets the needs of these patients. The present invention provides a contact lens which can be worn by the patient suffering from corneal instability following radial keratonomy. Similarly, the lens of the present invention can be worn by the radial keratonomy patient who seeks to improve his or her appearance by wearing contact lenses rather than eye glasses to correct astigmatism and other visual acuity defects uncorrected by the surgical procedure.
The present invention also provides a contact lens which may be fitted to a cornea having a generally flat central anterior surface resulting from other surgical procedures, such as corneal transplants used in treating corneal disease, in addition to radial keratonomy.